The present invention is generally directed to error correction and detection systems which are employable with character or symbol codes. More particularly, the present invention is related to a method and apparatus for providing a check character for an arbitrary sequence of information symbols. The invention also includes a system for decoding a received sequence of processed character symbols and for detecting the presence of an error in a single position amongst the received character symbol signals. Even more particularly, the present invention pertains to error correction and detection schemes usable with bar code systems.
In particular, it is known that bar codes are capable of providing a means for identification of objects in ways that do not require optical character recognition (OCR) of a plurality of alphanumeric or other symbols. In general, bar codes typically employ a series of stripes of varying widths in sequence to represent a particular character symbol. Also, as described in application Ser. No. 07/351,902 filed May 15, 1989, it is seen that one may employ bar codes which exhibit only a single width bar. Furthermore, it is seen that it is possible to construct such codes so as to employ built-in timing indications. While such codes are reliable, it is possible to employ such codes and other codes in environments in which there may be a certain undesirable degradation of reading accuracy. Accordingly, the present invention is directed to systems for encoding character symbols to provide for redundancy and error correction. In the present invention encoding and decoding systems are in fact employed at the symbol level rather than at the bit or bar level.
Furthermore, it is seen that the code of the present invention is applicable to any symbol based coding system. In particular, the present system is also applicable to OCR fonts. Coding systems of the present kind are therefore seen to be particularly valuable when symbol codes of any sort are employed in hostile environments in which high degrees of reading accuracy are not always achievable. Accordingly, it is seen that the system of the present invention is particularly applicable to the situation in which single width bar codes with built-in timing characteristics are employed in conjunction with the processing of silicon semiconductor wafers which are processed in harsh environments. It is further seen that the code of the present invention is applicable to any symbol based code and is not limited to bar codes or OCR fonts but may also be employed in conjunction with any code in which the bits or bars are grouped into subordinate packages. It is also applicable directly to ordinary symbol fonts where there is no subordinate representation of code symbols.